1 answer

This depends on your use of the forward slash. The answer will be different depending on whether you are using it as an "or" or an "and".

If you are using the forward slash in place of "or", e.g. a duty falls on Employer or Insurer, you should use a singular verb.

Conversely, if you are using the forward slash in place of "and", e.g. a duty falls on Employer and Insurer, then you should use a plural verb.

However, there is a rider to the second point. If you are discussing a specific instance or group where the Employer is the Insurer, for example a self-insuring employer, then you could correctly use a singular verb.